Heater structure

ABSTRACT

A heater for heat developing of imagable sheet materials comprising a rope heater, a heat-conductive, open-faced, arcuate platen wherein the platen has dual channels along its axial length for retaining the rope heater and heat conductive clips having a channel therein, which clips are attached to the ends of the platen for retaining the rope heater in conductive contact with the ends of the platen.

United States Patent 1191 1111 3,873,810 Larson Mar. 25, 1975 HEATER STRUCTURE 2,122,604 7/1938 Bridges 338/214 [75] Inventor: Roger L. Larson, Roseville, Minn. Hlcks 219/345 X [73] Assignee: Minnesota Mining and K d t 1 219/536 X nu sone a zgfi iz fi Company 3,786,230 1/1974 Brandenburg 219/345 Filedl 1974 Primary Exanziner-Volodymyr Y. Mayewsky [21] AppL No; 451 568 Attorney, Agent, or FirmAlexander, Sell, Steldt &

DeLaHunt [52] US. Cl 219/535, 219/345, 219/530, 57 AB CT 219/536, 219/540, 210/542 T [51] Int. Cl. H05b 3/58 A heater for heat developmg of magable Sheet mater" [58] Field of Search 219/345, 347, 352, 354, 315 comprising a rope heater 3 heabconductiva open' 219/358, 469 530 535, 536, 537 540 542 faced, arcuate platen wherein the platen has dual 338/213 channels along its axial length for retaining the rope heater and heat conductive clips having a channel [56] References Cited therein, which clips are attached to the ends of the UNITED STATES PATENTS platen for retaining the rope heater in conductive contact with the ends of the platen. 1,464,280 8/1923 Hynes 219/345 I 1,707,982 4/1929 Humphrey 219/358 X 2 Claims, 4 Drawing Figures BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to an improvement in the structure of a heater and in one aspect to an improved heating structure for a heat developable sheet processor.

2. Description of the Prior Art Several processes for forming visible images on sheet material require heat development. Heat is generally either applied to the sheet material itself to develop a latent image or applied to an assembly of the sheet material and either the original or an intermediate sheet to transfer the image to the sheet material. A useful device for providing the necessary heat for image development in processors comprises a heating platen in the form of an arcuateplate and a pressure member in the form of a rotatable cylindrical drive roll against which the heated surface of the platen is pressed. One such arcuate heating platen comprises a relatively thin arcuate heat-conductive plate which for convenience and economy of manufacture can be extruded. The extruded platen contains channels or grooves on the convex or outward side running along it axial lengthwherein an insulated, flexible, sheathed, resistance heating element, commonly termed a rope-heater" can be releasably retained. The platen specifically contains on its outward or convex surface two spaced channels extending axially along the length thereof for retaining a single rope type resistance heater in good heat conductive contact with the platen. The rope heater extends down both channels and is looped from one channel to the other. The heater ends meet at a central location along one of the channels for convenient electrical contact to a source conductor. The inward. concave or open face of the heat-conductive platen provides a heating surface to contact the sheet material or sheet assembly.

While such a heating platen is useful to rapidly provide development heat to sheet material, the heat provided can be of uneven intensity over the length of the heating platen. This nonuniformity of intensity can be traced to the fact that at the axial ends of the heating platen, where the single rope heater loops from one retaining channel to the other, no conductive contact is provided between the heat-conductive arcuate platen and the rope heater. Since image contrast is dependent on the quantity of heat reaching the sheet material in a short period of time, the image at the edge portions of the sheet material is not properly developed. Additionally, the rope heater, where looped over the ends of the heating platen between the channels, can be come overheated due to the lack of conduction of heat from it in these areas. This overheating prematurely reduces theeffectiveness and life of the heaters insulation covering.

By utilization of a heater structure of the present invention, this variation in heat intensity and resulting variation in image contrast can be substantially reduced. Similarly, the damaging effects to the rope heaters insulation covering by overheating can be minimized.

SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to pro vide an inexpensive heater structure, to improve present and future extruded heating platens and to evenly heat the entire surface area of sheet materials pressed against the platen. This is accomplished by utilization of heater retaining clips which can be releasably attached in heat conductive relationship, one on each end'of the extruded heating platen. These clips contain a rope heater retaining channel such that the rope heater can maintain heat conductive contact with the ends of the arcuate platen to heat the platen and cool the rope heater.

In this manner the developing heat is distributed to the ends of the heating platen such that the whole area of the heating surface receives even heat distribution and is maintained at a more uniform temperature.

Additionally, the heat retaining clips prevent overheating of the rope heater at the ends of the heating platen which can be deleterious to the insulating sheath of the rope heater.

DESCRIPTION OF THE DRAWING The present invention will be further understood after a perusal of the following detailed description which refers to the accompanying drawing wherein:

FIG. 1 is a perspective view of a heater structure formed according to the present invention;

FIG. 2 is a longitudinal fragmentary sectional view of the heater;

FIG. 3 is a prospective view of a rope heater retaining clip from the structure of FIG. 1; and

FIG. 4 is a cross-section of the arcuate platen taken at 4-4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawing, an arcuate heating platen 1 constructed according to the present invention is shown having a rope heater 3 attached thereto and containing at the ends a pair of rope heater retaining clips 4. The heating platen is comprised of an arcuate, heat conductive element 1 which can conveniently be an extrusion. An exemplary heat conductive material is aluminum. Along the axial length of arcuate element 1 are two channels, 2, for retaining rope heater 3 such that intimate heat conductive contact is maintained between the heater and platen. By utilizing dual channels, a single rope heater can be utilized with a convenient location for connection to an electrical source. Heater retaining clips 4 provide the necessary heat conductive path between the ends of the arcuate platen and the rope heater. Between the dual rope heater-retaining channels is a partially enclosed slot 8 whereby the heater retaining clips can be attached to the platen. FIG. 4 illustrates the dual rope heater retaining channels 2 and the partially enclosed slot 8 located between channels 2 for receiving the rope heater retaining clip 4.

The heater-retaining clips must, of course, be heat conductive so as to provide a heat path from the rope heater to the ends of the arcuate heating platen. Typically, the retaining clips can be ofthe same material as the arcuate platen itself.

As illustrated by FIG. 3, the clip 4 is a one piece structure having a channel 5, shapedlike channel 2, for receiving the rope heater in close contact. The clip is formed with a base 6 which affords a surface to contact the platen 1 in heat transfer conductive relationship,

3 and aleg .7 for engaging the end of platen 1. The retaining leg 7 is inserted in the slot 8 for releasably attaching the clip to arcuate platen 1. I

The member having the channel 5, and the members 6 and 7 can be formed from a single element or may be formed separately and joined together as for example by welding.

Attachment of the rope heater retaining clip to the arcuate platen can be accomplished by a variety of means. An exemplary method is that illustrated in FIG. 2. During extrusion of the arcuate heating platen, a cross section of which is illustrated in FIG. 4, a partially closed slot 8 can be provided in the platen between channels 2 for retaining the clip 4. Retaining leg 7 of the clip can then conveniently be provided asa relatively thin member having a bend in it running transverse to its length, such that the height of leg 7 is slightly larger than the height of the enclosed portion of the retaining slot 8 in the arcuate platen. The width of leg 7 should be such that the edges of leg 7 contact the enclosed portions of slot 8. During insertion of the clip into slot 8 of the platen, leg 7 is compressed slightly to thereby provide sufficient force to hold the clip to the ends of the heating platen.

Operation of the arcuate heating platen of my invention for image development provides a temperature variation over the entire length of the platen of only 4 about 5F A similar platen, but without utilizing the rope heater retaining clips, provides a temperature variation of about 15F.

What is claimed is:

l. A heater for heat developing sheet materials comprising an insulated, flexible, sheathed, electrical resistance heating element; an open-faced, arcuate heat conductive platen having spaced dual channels extending axially along the outward side of said platen receiving said heating element therein, said platen having a partially enclosed slot. along the axial length ofthe outward side thereof between said channels; and at least one heat-conductive clip attached to one end portion of said platen, said clip having a channel therein supporting said heating element, a surface contacting said platen, and a retaining leg having a bend therein transverse to the length of said leg such that the height of said leg is slightly greater than the height of the enclosed portions of said slot, said leg having a width sufficient to contact said enclosed portions of said slot whereby said platen is conductively heated by said heating element to more uniformely heat the sheet material.

2. The heater of claim 1 wherein said platen and said clip are aluminum. 

1. A heater for heat developing sheet materials comprising an insulated, flexible, sheathed, electrical resistance heating element; an open-faced, arcuate heat-conductive platen having spaced dual channels extending axially along the outward side of said platen receiving said heating element therein, said platen having a partially enclosed slot along the axial length of the outward side thereof between said channels; and at least one heat-conductive clip attached to one end portion of said platen, said clip having a channel therein supporting said heating element, a surface contacting said platen, and a retaining leg having a bend therein transverse to the length of said leg such that the height of said leg is slightly greater than the height of the enclosed portions of said slot, said leg having a width sufficient to contact said enclosed portions of said slot whereby said platen is conductively heated by said heating element to more uniformely heat the sheet material.
 2. The heater of claim 1 wherein said platen and said clip are aluminum. 